A King and Bishop alone cannot mate the lone King, but a King and two Bishops can. Therefor it is very important to assure that the King doesn’t capture one of the Bishops during the mating attempt.
In addition stalemate has to be avoided and we have to accomplish the mate within 50 moves, but after this lesson this should not be a problem.

The diagram on the left illustrates the most typical mating pattern. Other mating patterns are possible, but in general this is the mating pattern that you should try to accomplish.

White’s light-squared Bishop and the White King are covering all of the squares to which the Black King might retreat and Black has been checkmated by White’s dark-squared Bishop.

This second diagram illustrates one of the most important ideas of the mating process. The two Bishops have created a prison for the Black King and the King is unable to approach the Bishops. The White King is free to move.

Essentially White wins by forcing the Black King to the side of the board, then to a corner, and then checkmates.

We start from a rather difficult position in which the Bishop is attacked by the King and our own King is placed in a corner.

1.Bb4 Kd4 2.Kb7 Ke3 3.Bb5 and now we have placed the Bishops in such a way that the Black King is locked up within a large triangle. 3...Kd4 4.Kb6 Kd5

Not the fastests, but maybe easier to see 12.Be2+ because the size of the triangle is decreased again in the same way. 12...Kg3 13.Kf5 Kh3 14.Bf3 Kg3 15.Ke4 Kh3 16.Bf4 and the Black King can only move between h3 and h4. 16...Kh4 17.Ke3 Kh3 18.Kf2 Kh4 Now the Bishop is placed aside to enable Black’s King to move to h2. 19.Be2 Kh3 and taking away h4: 20.Bg5 Kh2 21.Bf1 Kh1 22.Bg2+ Kh2 23.Bf4#